conventional dryer or heater for blowing heated air as shown in FIG. 7 is formed by binding each PTC semiconductor heating element H in between two aluminum-plate frames A by adhesive S, each aluminum frame A confining a corrugated fin F within each frame A with the fin F fixed to the frame A by adhesive S such as by silicon adhesive, and each pair of terminals T connected to a power source being electrically connected to two poles of each PTC semiconductor heating element H for passing current through each PTC element H for heating air blown through the PTC elements H for heating purpose.
However, such a conventional dryer has the following drawbacks:
1. Due to different coefficients of heat expansion of the aluminum frame A and PTC element H, and due to the exposure of the silicon adhesive under high temperature to cause curing, breakage and cleavage of the adhesive binding, a sparking gap may occur between each PTC heating element H and each aluminum plate A to cause sparking, short-circuit or explosion hazards. The conducting surface on each PTC heating element H, as influenced by the silicon adhesive subjected to thermal shock when heated and cooled, may be easily oxidized to produce high impedance which in turn may cause partial over-current and over-heating of the PTC element, shortening the service life of PTC element or even explosion hazard thereof. PA1 2. The binding of PTC element with aluminum plate A or aluminum plate A with fin F should be processed or welded from point to point to increase production cost and quality control problems. PA1 3. The fin S forms a "point" contact with the aluminum plate A rather than a "surface" contact to thereby reduce the heat-exchange area and decrease the heating efficiency. Meanwhile, the "point" contact between the corrugated fin F with the aluminum plate A may be accumulated with dusts and dirts to increase wind resistance and decrease heat-exchange efficiency therefore. PA1 4. The aluminum plate A contacted with the PTC element H is directly secured with a terminal T which is connected to power source without any fuse. Once a short-circuit and sparking accident is caused, the PTC heater may be burned. During the manufacturing of the PTC elements, the clearance of thinner PTC element may be loosened in the assembly of PTC elements to produce sparking gap which may cause fire or explosion hazard of the PTC heater when passing current therethrough.
The present inventor has found the drawbacks of a conventional PTC dryer or heater, and invented the present cassette type PTC heating device.